Even with the new server, I am not receiving e-mails when a new user registers. I tried to solve this by monitoring registering users, but sadly, a spambot registers every 8 minutes on average, so this is not an option. I changed the message after registration to mention that a mail should be send to me to get an account activated, so hopefully that solves the issue.

In the meantime, if you registered recently, please send me an e-mail so I can activate your account manually.

The section is found in the ACP >> Users and Groups >> Custom profile fields. Setting it to "Display on registration screen" and be a "Required field" should be enough to make it a required entry on registration.

The question could be related to ompf/ray tracing in some way, or something simple like what's 3x4. Or maybe "What's the surface area of a unit sphere in steradians" .